Mailing machines for printing postage indicia on envelopes and other forms of mail pieces have long been well known and have enjoyed considerable commercial success. There are many different types of mailing machines, ranging from relatively small units that handle only one mail piece at a time, to large, multi-functional units that can process hundreds of mail pieces per hour in a continuous stream operation. The larger mailing machines often include different modules that automate the processes of producing mail pieces, each of which performs a different task on the mail piece. The mail piece is conveyed downstream utilizing a transport mechanism, such as rollers or a belt, to each of the modules. Such modules could include, for example, a singulating module, i.e., separating a stack of mail pieces such that the mail pieces are conveyed one at a time along the transport path, a moistening/sealing module, i.e., wetting and closing the glued flap of an envelope, a weighing module, and a metering module, i.e., applying evidence of postage to the mail piece. The exact configuration of the mailing machine is, of course, particular to the needs of the user.
Typically, a control device, such as, for example, a microprocessor, performs user interface and controller functions for the mailing machine. Specifically, the control device provides all user interfaces, executes control of the mailing machine and print operations, calculates postage for debit based upon rate tables, provides the conduit for the Postal Security Device (PSD) to transfer postage indicia to the printer, operates with peripherals for accounting, printing and weighing, and conducts communications with a data center for postage funds refill, software download, rates download, and market-oriented data capture. The control device, in conjunction with an embedded PSD, constitutes the system meter that satisfies U.S. information-based indicia postage (IBIP) meter requirements and other international postal regulations regarding closed system meters. The United States Postal Service (USPS) initiated the Information-Based Indicia Program (IBIP) to enhance the security of postage metering by supporting new methods of applying postage to mail. The USPS has published draft specifications for the IBIP. The requirements for a closed system are defined in the “Performance Criteria for Information-Based Indicia and Security Architecture for Closed IBI Postage Metering System (PCIBI-C), dated Jan. 12, 1999. A closed system is a system whose basic components are dedicated to the production of information-based indicia and related functions, similar to an existing, traditional postage meter. A closed system, which may be a proprietary device used alone or in conjunction with other closely related, specialized equipment, includes the indicia print mechanism.
The PCIBI-C specification defines the requirements for the indicium to be applied to mail produced by closed systems. The indicium consists of a two-dimensional (2D) barcode and certain human-readable information. Some of the data included in the barcode includes, for example, the PSD manufacturer identification, PSD model identification, PSD serial number, values for the ascending and descending registers of the PSD, postage amount, and date of mailing. In addition, a digital signature is required to be created by the PSD for each mail piece and placed in the digital signature field of the barcode. Several types of digital signature algorithms are supported by the IBIP, including, for example, the Digital Signature Algorithm (DSA), the Rivest Shamir Adleman (RSA) Algorithm, and the Elliptic Curve Digital Signature Algorithm (ECDSA).
Thus, for each mail piece the PSD must generate the indicium, including computing the digital signature to be included in the indicium, once the relevant data needed for the indicium generation are passed into the PSD. The generated indicium can then be printed on a mail piece. Typically, to reduce the risk of lost funds, the debiting of the postage value for the generated indicium is delayed until just before the printing of the indicium begins. In this manner, if the mail piece does not reach the printing area, such as, for example, due to a jam or other malfunction, and the indicium is not printed, there are no funds deducted for the indicium that is not printed. Thus, the debit operation is preferably not performed until the mail piece on which the indicium is to be printed has passed a “point of no return,” thereby providing some assurance that printing of the indicium will occur.
FIG. 1 illustrates a timing diagram for a conventional mailing machine used to print indicia on mailing machines. As illustrated, the timing includes a succession of cryptographic processing intervals and printing intervals. The cryptographic processing for a first mail piece (Mailpiece #1) begins when the amount of desired postage is entered by an operator (Set Postage). Printing of the first mail piece, and debiting for the funds included in the indicium, occur when the first mail piece reaches the printing area (First Mailpiece Present). Thus, as illustrated, there may be some delay (idle time) between the time the cryptographic processing for the first mail piece has been completed and the printing begins. This delay is typically due to the amount of time it may take for the operator to place the mail piece (or stack of mail pieces if processing a batch) into the input of the mailing machine and/or the time required to transport the mail piece from the input of the mailing machine to the printing area. In the processing illustrated by FIG. 1, the cryptographic processing for an indicium for the next mail piece (Mailpiece #2) does not begin until printing of the indicium on the current mail piece (Mailpiece #1) has been completed. Since the generation of the indicium, including computation of the digital signature, requires a predetermined amount of time, as well as printing each indicium, the throughput of a mailing machine utilizing the timing illustrated in FIG. 1 is limited by these time constraints. Specifically, the number of mail pieces that the mailing machine can process per hour is constrained by the total cycle time for each mail piece, i.e., the amount of time required to generate and print an indicium.
The throughput of mailing machines has been improved by implementing the processing in a pipelined fashion as illustrated in FIG. 2. As shown in FIG. 2, the cryptographic processing for the first mail piece (Mailpiece #1) is similar as that described with respect to FIG. 1 above; however, the cryptographic processing for the next mail piece (Mailpiece #2) begins after the debit operation is performed for the first mail piece (Mailpiece #1) and while the first mail piece is being printed with the indicium just generated. Thus, as compared with the processing as illustrated in FIG. 1, the number of mail pieces that can be processed in the same amount of time is increased, thereby increasing the throughput of the mailing machine.
There are, however, still some limitations with the processing as illustrated in FIG. 2. The throughput of the mailing machine is directly proportional to the most time consuming of the steps involved, i.e., the time delay required for the cryptographic processing. For smaller mailing machines that do not have high throughput, the time delay associated with such generation and computation does not limit the throughput, i.e., the calculations are performed quickly enough and therefore are not a limiting factor for the throughput. For larger mailing machines with higher throughputs, however, the speed of cryptographic processing may be the limiting factor with respect to the throughput of the mailing machine. Several methods have been devised to increase the throughput of mailing machines constrained by the speed of cryptographic processing. One such method includes performing parts of the cryptographic operation not dependent upon actual characteristics of the mail piece prior to knowing those characteristics, e.g., calculating the r value in a Digital Signature Algorithm (DSA) indicium. Another method includes pre-computing large numbers of indicia, including performing accounting for these indicia, of different values and storing them for future use. While both of these methods increase the throughput, there are some drawbacks. For example, performing parts of the cryptographic processing does not take advantage of all “unused” time in mail processing, i.e., time when the cryptographic processor is normally idle. Pre-computing large numbers of indicia of different values and storing them requires large amounts of memory and sophisticated bookkeeping to track the indicia that have been used.
Thus, there exists a need for a method and system that increases the throughput of a mailing machine.